Method and system for determining knock control fluid composition

ABSTRACT

Methods and systems are provided for accurately determining the composition of a knock control fluid using sensors already present in the engine system. An intake oxygen sensor is used to estimate the water and the alcohol content of a knock control fluid that is direct injected into an engine cylinder responsive to an indication of abnormal combustion. A change in the pumping current of the oxygen sensor due to the water content of the knock control fluid is distinguished from a change in the pumping current of the oxygen sensor due to the alcohol content of the knock control fluid, while compensating for interfering effects of intake air diluents on the change in pumping current.

FIELD

The present description relates generally to methods and systems for determining the composition of a wiper fluid injected into an engine for knock control.

BACKGROUND/SUMMARY

A variety of knock control fluids have been developed to mitigate abnormal combustion events, including various combinations of gasoline, ethanol, methanol, other alcohols, water, and other inert fluids. Water injection, for example, reduces knock, provides charge cooling, and reduces the octane requirement. In addition, since water injection can also be used for engine dilution control, the need for a dedicated knock control fluid is reduced.

Another example of a knock control fluid is shown by Surnilla in U.S. Pat. No. 7,533,651. Therein, direct injection of a washer fluid, which includes water and alcohol (e.g., engine coolant or methanol) leverages the charge cooling properties of the both the fluid and the direct injection to reduce knock. In addition to protecting the water from freezing, the inclusion of engine coolant in the composition of the injected knock control fluid offers an added advantage of having light hydrocarbons (such as methanol), which help in the combustion process. The overall approach increases engine efficiency while reducing the octane requirement of injected fuel, thereby increasing the power output of the engine. Herein, the wiper fluid can be repurposed for knock control in addition to being used for cleaning a vehicle windshield.

However, the inventors herein have recognized an issue with the approach. There may be variations in windshield wiper fluid composition. For example, there may be a wide variation in the ethanol or methanol content of the fluid, as such. In addition, when a windshield wiper fluid tank is refilled, based on an amount and composition of wiper fluid that was left over in the tank, the composition of the available wiper fluid following the refilling may vary. While this does not affect the fluid's ability to clean a windshield wiper, it may affect the knock controlling ability of the fluid. For example, the octane value of the fluid may change. As such, various engine parameters are adjusted based on the injected knock control fluid. For example, based on the alcohol content of the injected fluid, cylinder fueling may be adjusted. In addition, engine parameters may need to be adjusted based on the type of alcohol in the fluid (e.g., whether the alcohol is ethanol or methanol). As a result, errors in the estimation of a wiper fluid composition can result in significant air-fuel errors, degrading engine performance. Further, if the composition of a wiper fluid is not accurately known, use of wiper fluid as a knock control fluid may be limited. On the other hand, the addition of a sensor dedicated to estimating the alcohol content and composition of a knock control fluid may add significant cost and complexity. While an intake oxygen sensor may be used to estimate the alcohol content of the knock control fluid during selected conditions, the inventors have recognized that the presence of diluents such as humidity, positive crankcase ventilation (PCV) hydrocarbons, and purge gases can cause errors in the output of the intake oxygen sensor, corrupting the estimation.

In one example, the issues described above may be addressed by a method for an engine comprising: injecting a water-alcohol blend into an engine intake initially at a first flow rate and then at a second, different flow rate; applying a reference voltage to an oxygen sensor and monitoring a change in pumping current of the sensor following each injecting; learning a first portion of the change in pumping current due to a water content of the blend; learning a second portion of the change in pumping current due to an alcohol content of the blend; and learning a third portion of the change in pumping current due to diluents in intake air. In this way, the composition of a knock control fluid injected into an engine can be accurately determined using an existing oxygen sensor, such as an intake or an exhaust oxygen sensor, with noise factors being mitigated.

As an example, following refilling of a wiper fluid tank, a wiper fluid composition may be estimated using an intake oxygen sensor. The wiper fluid may then be used as a knock control fluid. As such, the wiper fluid may include a mixture of water and alcohol but no gasoline. Further, an alcohol type in the fluid may be known a priori. For example, it may be known that the wiper fluid is a water-ethanol mixture, or a water-methanol mixture. However, a ratio of water to the specified alcohol in the fluid may not be accurately known. A controller may first inject the knock control fluid at a first gaseous volume percent into the intake manifold, downstream of an intake throttle and upstream of an intake oxygen sensor. The fluid may be injected while EGR is disabled to reduce interference on the results from EGR. A lower reference voltage (e.g., 450 mV) may then be applied to the intake oxygen sensor and an output of the sensor may be noted. For example, a first pumping current may be output. The controller may then inject the knock control fluid at a second, different gaseous volume percent into the intake manifold. The different volume percentages may be provided by injecting different amounts of the fluid at a given air mass flow rate, or by injecting a given amount of the fluid at different air as flow rates. The lower reference voltage (e.g., 450 mV) is then reapplied to the intake oxygen sensor and a second output of the sensor may be noted. For example, a second pumping current may be output. As such, the pumping currents may be affected by a reduction in the oxygen concentration at the oxygen sensor due to the water content of the knock control fluid as well as due to the alcohol content of the knock control fluid, and further due to the presence of diluents, such as PCV gas hydrocarbons, in the intake air. Specifically, the water in the knock control fluid may have a dilution effect on the oxygen sensor while the alcohol in the knock control fluid and the diluent hydrocarbons in the intake air may combust with oxygen at the sensor, reducing the oxygen concentration estimated at the sensor. An engine controller may normalize the first and second pumping currents based on the corresponding injection mass flow rates and then learn a common offset in the first and second pumping currents due to the presence of diluents in the intake air. After adjusting for the diluents, the controller may calculate the alcohol content of the knock control fluid based on the first and second normalized pumping currents, as well as the injection mass. For example, the engine controller may reference a 3D calibration map to estimate the alcohol content of the fluid, and update the composition of the fluid. By learning the composition of the fluid, the flexibility of usage of the wiper fluid as a knock control fluid may be enhanced.

It will be appreciated that while the above example discusses washer fluid composition estimation using an intake oxygen sensor, in alternate examples, the estimation may be performed using an exhaust gas oxygen sensor (such as a UEGO). Therein, the fluid may be injected at the first and second gaseous volume percent during deceleration fuel shut-off (DFSO) conditions and the composition may be determined based on a change in the pumping current of the UEGO.

In this way, an existing intake or exhaust oxygen sensor can be used to estimate the composition (including the hydrocarbon type and alcohol content) of a knock control fluid while compensating for corruption of results by intake air diluents. The technical effect of monitoring the output of an intake oxygen sensor after injecting fluid at different volume percentages is that a change in the pumping current of the sensor that is attributed to the water component of the knock control fluid can be better distinguished from the change attributed to the alcohol component of the knock control fluid without requiring adjustments to EGR, purge or PCV flow to reduce noise. This is due to the fact that the dilution effect on the oxygen sensor has a remarkably different contribution than the combustion effect of the alcohol. In addition, a common diluent based offset may be learned because the diluents cause a similar relative change in the pumping current at the different volume percentage rates. By better estimating the composition of an injected knock control fluid, the use of the knock control fluid may be expanded to engines of different fuel types, improving the robustness of the system. In addition, the accuracy of fuel octane estimates may be increased, which allows spark control to be improved. For example, spark retard usage for knock control may be reduced providing fuel economy benefits. By learning the noise in the pumping currents cause by the presence of intake air diluents, the knock control fluid can be estimated accurately even when purge or EGR is present. By using an existing intake oxygen sensor to determine the composition of the knock control fluid, the need for a dedicated sensor is reduced without compromising on the accuracy of the estimation.

It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an engine system.

FIG. 2 shows a detailed diagram of an engine combustion chamber.

FIG. 3 shows a schematic diagram of an example intake oxygen sensor.

FIG. 4 shows a flow chart illustrating a routine for using an intake oxygen sensor for knock control fluid alcohol estimation while compensating for interference from intake air diluents.

FIG. 5 shows a map demonstrating an example relationship between an alcohol content of a knock control fluid relative and each of a change in the pumping current of an oxygen sensor, and a mass of the knock control fluid injected into an engine, before compensating for the effect of diluents.

FIG. 6 shows a map demonstrating an example relationship between an air mass flow rate at which a knock control fluid is injected and an estimated alcohol concentration of the knock control fluid based on an intake oxygen sensor output, the map used for determining an offset for compensating for the effect of diluents on the output of the intake oxygen sensor.

FIG. 7 shows a flow chart illustrating a routine for using an exhaust oxygen sensor for knock control fluid alcohol estimation while compensating for interference from intake air diluents.

FIG. 8 shows a map demonstrating the relationship between the molar oxygen percentage estimated by an exhaust oxygen sensor and the molar percentage of washer fluid in an intake air stream.

DETAILED DESCRIPTION

The following description relates to systems and methods for determining the composition of a knock control fluid injected into an engine, such as the engine of FIGS. 1-2, based on outputs from an intake or exhaust oxygen sensor, such as the sensor of FIG. 3. As such, the oxygen sensor may be used during different engine operating conditions to estimate the alcohol content of a fuel delivered to the engine during engine combustion, or the alcohol composition of the knock control fluid delivered to the engine responsive to an indication of knock (FIG. 3). An engine controller may be configured to perform a control routine, such as the example routine of FIGS. 4 and 7, to estimate the composition of the knock control fluid, including the alcohol content and the hydrocarbon content of the fluid, based on a relative change in the pumping current of the oxygen sensor following injection of the fluid at different injection rates. The controller may reference a map, such as the example map of FIGS. 5-6 and 8, to correlate the change in pumping current and the injection mass with the alcohol content of the injected fluid. One or more engine operating parameters such as spark timing and/or fuel injection amount may be adjusted based on the determined composition of the knock control fluid. In this manner, engine knock control fluid usage may be expanded.

FIG. 1 shows a schematic depiction of an example turbocharged engine system 100 including a multi-cylinder internal combustion engine 10 and twin turbochargers 120 and 130. As one non-limiting example, engine system 100 can be included as part of a propulsion system for a passenger vehicle. Engine system 100 can receive intake air via intake passage 140. Intake passage 140 can include an air filter 156 and an EGR throttle valve 131. Engine system 100 may be a split-engine system wherein intake passage 140 is branched downstream of EGR throttle valve 131 into first and second parallel intake passages, each including a turbocharger compressor. Specifically, at least a portion of intake air is directed to compressor 122 of turbocharger 120 via a first parallel intake passage 142 and at least another portion of the intake air is directed to compressor 132 of turbocharger 130 via a second parallel intake passage 144 of the intake passage 140.

The first portion of the total intake air that is compressed by compressor 122 may be supplied to intake manifold 160 via first parallel branched intake passage 146. In this way, intake passages 142 and 146 form a first parallel branch of the engine's air intake system. Similarly, a second portion of the total intake air can be compressed via compressor 132 where it may be supplied to intake manifold 160 via second parallel branched intake passage 148. Thus, intake passages 144 and 148 form a second parallel branch of the engine's air intake system. As shown in FIG. 1, intake air from intake passages 146 and 148 can be recombined via a common intake passage 149 before reaching intake manifold 160, where the intake air may be provided to the engine.

A first EGR throttle valve 131 may be positioned in the engine intake upstream of the first and second parallel intake passages 142 and 144, while a second air intake throttle valve 158 may be positioned in the engine intake downstream of the first and second parallel intake passages 142 and 144, and downstream of the first and second parallel branched intake passages 146 and 148, for example, in common intake passage 149.

In some examples, intake manifold 160 may include an intake manifold pressure sensor 182 for estimating a manifold pressure (MAP) and/or an intake manifold temperature sensor 183 for estimating a manifold air temperature (MCT), each communicating with controller 12. Intake passage 149 can include a charge air cooler (CAC) 154 and/or a throttle (such as second throttle valve 158). The position of throttle valve 158 can be adjusted by the control system via a throttle actuator (not shown) communicatively coupled to controller 12. An anti-surge valve 152 may be provided to selectively bypass the compressor stages of turbochargers 120 and 130 via bypass passage 150. As one example, anti-surge valve 152 can open to enable flow through bypass passage 150 when the intake air pressure upstream of the compressors attains a threshold value.

Intake manifold 160 may further include an intake gas oxygen sensor 172. In one example, the oxygen sensor is a UEGO sensor, such as the example UEGO sensor of FIG. 3. As elaborated herein, the intake gas oxygen sensor may be configured to provide an estimate regarding the oxygen content of fresh air received in the intake manifold. In addition, when EGR is flowing, a change in oxygen concentration at the sensor may be used to infer an EGR amount and used for accurate EGR flow control. Further still, during selected fueling conditions, the reference voltage of the sensor may be modulated and the corresponding change in current may be used to infer the alcohol content of an injected fuel. As also elaborated herein, during selected engine fueling conditions, a knock control fluid is injected at different injection flow rates (or volume percentages), following which the reference voltage is applied to the sensor. Based on the corresponding change in current, a controller may infer and distinguish the water content of the injected fluid from the alcohol content of the injected fluid. In the depicted example, oxygen sensor 162 is positioned upstream of throttle 158 and downstream of charge air cooler 154. However, in alternate embodiments, the oxygen sensor may be positioned upstream of the CAC.

A pressure sensor 174 may be positioned alongside the oxygen sensor for estimating an intake pressure at which an output of the oxygen sensor is received. Since the output of the oxygen sensor is influenced by the intake pressure, a reference oxygen sensor output may be learned at a reference intake pressure. In one example, the reference intake pressure is a throttle inlet pressure (TIP) where pressure sensor 174 is a TIP sensor. In alternate examples, the reference intake pressure is a manifold pressure (MAP) as sensed by MAP sensor 182.

Engine 10 may include a plurality of cylinders 14. In the depicted example, engine 10 includes six cylinders arrange in a V-configuration. Specifically, the six cylinders are arranged on two banks 13 and 15, with each bank including three cylinders. In alternate examples, engine 10 can include two or more cylinders such as 3, 4, 5, 8, 10 or more cylinders. These various cylinders can be equally divided and arranged in alternate configurations, such as V, in-line, boxed, etc. Each cylinder 14 may be configured with a fuel injector 166. In the depicted example, fuel injector 166 is a direct in-cylinder injector. However, in other examples, fuel injector 166 can be configured as a port based fuel injector.

Intake air supplied to each cylinder 14 (herein, also referred to as combustion chamber 14) via common intake passage 149 may be used for fuel combustion and products of combustion may then be exhausted from via bank-specific parallel exhaust passages. In the depicted example, a first bank 13 of cylinders of engine 10 can exhaust products of combustion via a first parallel exhaust passage 17 and a second bank 15 of cylinders can exhaust products of combustion via a second parallel exhaust passage 19. Each of the first and second parallel exhaust passages 17 and 19 may further include a turbocharger turbine. Specifically, products of combustion that are exhausted via exhaust passage 17 can be directed through exhaust turbine 124 of turbocharger 120, which in turn can provide mechanical work to compressor 122 via shaft 126 in order to provide compression to the intake air. Alternatively, some or all of the exhaust gases flowing through exhaust passage 17 can bypass turbine 124 via turbine bypass passage 123 as controlled by wastegate 128. Similarly, products of combustion that are exhausted via exhaust passage 19 can be directed through exhaust turbine 134 of turbocharger 130, which in turn can provide mechanical work to compressor 132 via shaft 136 in order to provide compression to intake air flowing through the second branch of the engine's intake system. Alternatively, some or all of the exhaust gas flowing through exhaust passage 19 can bypass turbine 134 via turbine bypass passage 133 as controlled by wastegate 138.

In some examples, exhaust turbines 124 and 134 may be configured as variable geometry turbines, wherein controller 12 may adjust the position of the turbine impeller blades (or vanes) to vary the level of energy that is obtained from the exhaust gas flow and imparted to their respective compressor. Alternatively, exhaust turbines 124 and 134 may be configured as variable nozzle turbines, wherein controller 12 may adjust the position of the turbine nozzle to vary the level of energy that is obtained from the exhaust gas flow and imparted to their respective compressor. For example, the control system can be configured to independently vary the vane or nozzle position of the exhaust gas turbines 124 and 134 via respective actuators.

Exhaust gases in first parallel exhaust passage 17 may be directed to the atmosphere via branched parallel exhaust passage 170 while exhaust gases in second parallel exhaust passage 19 may be directed to the atmosphere via branched parallel exhaust passage 180. Exhaust passages 170 and 180 may include one or more exhaust after-treatment devices, such as a catalyst, and one or more exhaust gas sensors 228.

In one example, exhaust gas sensor 228 is an oxygen sensor such as a UEGO sensor. An example embodiment of the UEGO sensor is provided at FIG. 3. As elaborated herein, the exhaust gas oxygen sensor may be used to estimate the oxygen content of exhaust in the intake manifold and infer an air-fuel ratio (AFR) amount for accurate AFR control. Further still, during selected engine non-fueling conditions, the reference voltage of the sensor may be modulated and the corresponding change in current may be used to infer the alcohol content of a combusted fuel. As also elaborated herein, during selected non-fueling conditions, a knock control fluid may be injected at different injection flow rates (or volume percentages), and the reference voltage of the sensor may be applied. Based on the resulting change in current, a controller may infer and distinguish the water content of the injected fluid from the alcohol content of the injected fluid.

Engine 10 may further include one or more exhaust gas recirculation (EGR) passages, or loops, for recirculating at least a portion of exhaust gas from the exhaust manifold to the intake manifold. These may include high-pressure EGR loops for proving high-pressure EGR (HP-EGR) and low-pressure EGR-loops for providing low-pressure EGR (LP-EGR). In one example, HP-EGR may be provided in the absence of boost provided by turbochargers 120, 130, while LP-EGR may be provided in the presence of turbocharger boost and/or when exhaust gas temperature is above a threshold. In still other examples, both HP-EGR and LP-EGR may be provided simultaneously.

In the depicted example, engine 10 may include a low-pressure EGR loop 202 for recirculating at least some exhaust gas from the first branched parallel exhaust passage 170, downstream of the turbine 124, to the first parallel intake passage 142, upstream of the compressor 122. In some embodiments, a second low-pressure EGR loop (not shown) may be likewise provided for recirculating at least some exhaust gas from the second branched parallel exhaust passage 180, downstream of the turbine 134, to the second parallel intake passage 144, upstream of the compressor 132. LP-EGR loop 202 may include LP-EGR valve 204 for controlling an EGR flow (i.e., an amount of exhaust gas recirculated) through the loops, as well as an EGR cooler 206 for lowering a temperature of exhaust gas flowing through the EGR loop before recirculation into the engine intake. Under certain conditions, the EGR cooler 206 may also be used to heat the exhaust gas flowing through LP-EGR loop 202 before the exhaust gas enters the compressor to avoid water droplets impinging on the compressors.

Engine 10 may further include a first high-pressure EGR loop 208 for recirculating at least some exhaust gas from the first parallel exhaust passage 17, upstream of the turbine 124, to intake manifold 160, downstream of intake throttle 158. Likewise, the engine may include a second high-pressure EGR loop (not shown) for recirculating at least some exhaust gas from the second parallel exhaust passage 18, upstream of the turbine 134, to the second branched parallel intake passage 148, downstream of the compressor 132. EGR flow through HP-EGR loops 208 may be controlled via HP-EGR valve 210.

A PCV port 102 may be configured to deliver crankcase ventilation gases (blow-by gases) to the engine intake manifold along second parallel intake passage 144. In some embodiments, flow of PCV air through PCV port 102 may be controlled by a dedicated PCV port valve. Thus, when the PCV valve is closed, crankcase ventilation to the engine intake is disabled. Likewise, a purge port 104 may be configured to deliver purge gases from a fuel system canister to the engine intake manifold along passage 144. In some embodiments, flow of purge air through purge port 104 may be controlled by a dedicated purge port valve. Thus, when the purge valve is closed, fuel vapor purging to the engine intake is disabled

Humidity sensor 112 and pressure sensor 114 may be included in only one of the parallel intake passages (herein, depicted in the first parallel intake air passage 142 but not in the second parallel intake passage 144), downstream of EGR throttle valve 131. Specifically, the humidity sensor and the pressure sensor may be included in the intake passage not receiving the PCV or purge air. Humidity sensor 112 may be configured to estimate a relative humidity of the intake air. In one embodiment, humidity sensor 112 is an oxygen sensor configured to estimate the relative humidity of the intake air based on the output of the sensor at one or more voltages. Since purge air and PCV air can confound the results of the humidity sensor, the purge port and PCV port are positioned in a distinct intake passage from the humidity sensor. Pressure sensor 114 may be configured to estimate a pressure of the intake air. In some embodiments, a temperature sensor may also be included in the same parallel intake passage, downstream of the EGR throttle valve 131.

Intake oxygen sensor 172 may be used, during selected conditions, for estimating an intake oxygen concentration and inferring an amount of EGR dilution at the engine based on a change in the intake oxygen concentration upon opening of the EGR valve 204. For example, upon applying a reference voltage (Vs) to the sensor, a pumping current (Ip) is output by the sensor. The change in oxygen concentration may be proportional to the change in pumping current (delta Ip) output by the sensor. Likewise, during other selected conditions, intake oxygen sensor 172 may be used for estimating the water content of intake charge (that is, ambient humidity) or the water content of an injected fuel (and inferring the alcohol content of the injected fuel). Further still, as elaborated herein, during other conditions, the intake oxygen sensor may be used for estimating the water content and alcohol content of a knock control fluid and estimating a composition of the knock control fluid accordingly. In one example, the knock control fluid is a wiper fluid and is injected into the intake manifold at two or more different injection flow rates to provide distinct volume percentages. The reference voltage (Vs) may be applied to the sensor and a change in pumping current (Ip) output by the sensor may be learned following each injection at the different injection flow rates. A first portion of the change in pumping current (delta Ip) output by the sensor that is due to the water content of the injected knock control fluid may be learned, and distinguished from a second portion of the change in pumping current that is due to the alcohol content of the injected knock control fluid. In addition, by learning the change in pumping currents at two distinct injection flow rates, a common offset in the pumping currents resulting from the presence of diluents and other hydrocarbons interfering with the reaction at the oxygen sensor's sensing element may be learned, and used to correct the pumping currents, without requiring any change in EGR, purge or PCV flow during the estimation.

The position of intake and exhaust valves of each cylinder 14 may be regulated via hydraulically actuated lifters coupled to valve pushrods, or via a direct acting mechanical bucket system in which cam lobes are used. In this example, at least the intake valves of each cylinder 14 may be controlled by cam actuation using a cam actuation system. Specifically, the intake valve cam actuation system 25 may include one or more cams and may utilize variable cam timing or lift for intake and/or exhaust valves. In alternative embodiments, the intake valves may be controlled by electric valve actuation. Similarly, the exhaust valves may be controlled by cam actuation systems or electric valve actuation.

Engine system 100 may be controlled at least partially by a control system 15 including controller 12 and by input from a vehicle operator via an input device (not shown). Control system 15 is shown receiving information from a plurality of sensors 16 (various examples of which are described herein at FIG. 1 and FIG. 2) and sending control signals to a plurality of actuators 81. As one example, sensors 16 may include humidity sensor 112, intake air pressure sensor 114, MAP sensor 182, MCT sensor 183, TIP sensor 174, UEGO 228, and intake air oxygen sensor 172. In some examples, common intake passage 149 may further include a throttle inlet temperature sensor for estimating a throttle air temperature (TCT). In other examples, one or more of the EGR passages may include pressure, temperature, and air-to-fuel ratio sensors, for determining EGR flow characteristics. As another example, actuators 81 may include fuel injector 166, HP-EGR valves 210 and 220, LP-EGR valves 204 and 214, throttle valves 158 and 131, and wastegates 128, 138. Other actuators, such as a variety of additional valves and throttles, may be coupled to various locations in engine system 100, such as those described with reference to FIG. 2. The controller 12 receives signals from the various sensors of FIG. 1 (and FIG. 2) and employs the various actuators of FIG. 1 (and FIG. 2) to adjust engine operation based on the received signals and instructions stored on a memory of the controller. For example, controller 12 may receive input data from the various sensors, process the input data, and trigger the actuators in response to the processed input data based on instruction or code programmed therein corresponding to one or more routines. Example control routines are described herein with regard to FIGS. 4 and 7.

FIG. 2 depicts a detailed embodiment of a combustion chamber, such as a combustion chamber of engine 10 of FIG. 1. Components previously introduced in FIG. 1 are numbered similarly and not reintroduced.

Engine 10 may receive control parameters from a control system including controller 12 and input from a vehicle operator 230 via an input device 232. In this example, input device 232 includes an accelerator pedal and a pedal position sensor 234 for generating a proportional pedal position signal PP. Cylinder (herein also “combustion chamber’) 14 of engine 10 may include combustion chamber walls 236 with piston 238 positioned therein. Piston 238 may be coupled to crankshaft 240 so that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft 240 may be coupled to at least one drive wheel of the passenger vehicle via a transmission system. Further, a starter motor may be coupled to crankshaft 240 via a flywheel to enable a starting operation of engine 10.

Engine 10 is coupled in a vehicle system 100 that includes a windshield wiper system that enables cleaning of a vehicle windshield 68. Windshield 68 may be a front or rear windshield of a vehicle. The windshield wiper system includes at least one windshield wiper 70 operated by wiper motor 72. In response to an operator demand, and based on input from controller 12, wiper motor 72 may be energized causing wiper 70 to make multiple sweeping cycles known as wipes or sweeps over windshield 68. The wipes or sweeps enable wiper blade 71 to remove moisture, debris, and foreign particles from the surface of windshield 68. While operating wiper motor 72 and while wiper blade 71 is sweeping, based on request from a vehicle operator, controller 12 may intermittently inject or squirt a wiper fluid onto the windshield via wiper injector 74. Wiper fluid may be stored in a reservoir 76 from where it is delivered to the windshield. As elaborated herein, reservoir 76 may be further coupled to the intake passage as well as the engine cylinder. This allows the wiper fluid to be injected to provide knock control in addition to being used for windshield wiping purposes. Specifically, the wiper fluid may be injected into the intake manifold, specifically into intake passage 246, downstream of the intake throttle, during knock conditions, thereby enabling the windshield wiper fluid to be used as a knock control fluid. Additionally, or alternatively, windshield wiper fluid may be directly injected into an engine cylinder via direct injector, such as via the direct fuel injector or a dedicated direct fuel injector, to provide knock control. The wiper fluid stored in reservoir 76 may include a combination of water and alcohol, such as methanol or isopropanol. However, the wiper fluid does not contain any gasoline.

As such, there may be significant variation in the water: alcohol content of the wiper fluid. To enable the wiper fluid to be reliably used as a knock control fluid, a composition of the wiper fluid may need to be known. As elaborated with reference to FIG. 1, during selected conditions, such as immediately after the wiper fluid reservoir has been refilled, an intake oxygen sensor, such as sensor 172, may be used to estimate the water to alcohol content of the wiper fluid. Alternatively, an exhaust gas oxygen sensor, such as sensor 228, may be used to estimate the water to alcohol content of the wiper fluid. Example methods for estimating a wiper fluid composition using an intake or exhaust oxygen sensor is shown with reference to FIGS. 4 and 7.

Cylinder 14 can receive intake air via a series of intake air passages 242, 244, and 246. Intake air passage 246 may communicate with other cylinders of engine 10 in addition to cylinder 14. In some embodiments, one or more of the intake passages may include a boosting device such as a turbocharger or a supercharger. For example, FIG. 2 shows engine 10 configured with a turbocharger including a compressor 274 arranged between intake passages 242 and 244, and an exhaust turbine 276 arranged along exhaust passage 248. Compressor 274 may be at least partially powered by exhaust turbine 276 via a shaft 280 where the boosting device is configured as a turbocharger. However, in other examples, such as where engine 10 is provided with a supercharger, exhaust turbine 276 may be optionally omitted, where compressor 274 may be powered by mechanical input from a motor or the engine. A throttle 262 including a throttle plate 264 may be provided along an intake passage of the engine for varying the flow rate and/or pressure of intake air provided to the engine cylinders. For example, throttle 262 may be disposed downstream of compressor 274 as shown in FIG. 2, or alternatively may be provided upstream of compressor 274.

Exhaust passage 248 may receive exhaust gases from other cylinders of engine 10 in addition to cylinder 14. Exhaust gas sensor 228 is shown coupled to exhaust passage 248 upstream of emission control device 278. Sensor 228 may be selected from among various suitable sensors for providing an indication of exhaust gas air/fuel ratio such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO (as depicted), a HEGO (heated EGO), a NOx, HC, or CO sensor, for example. Emission control device 278 may be a three way catalyst (TWC), NOx trap, various other emission control devices, or combinations thereof.

Exhaust temperature may be measured by one or more temperature sensors (not shown) located in exhaust passage 248. Alternatively, exhaust temperature may be inferred based on engine operating conditions such as speed, load, air-fuel ratio (AFR), spark retard, etc. Further, exhaust temperature may be computed by one or more exhaust gas sensors 228. It may be appreciated that the exhaust gas temperature may alternatively be estimated by any combination of temperature estimation methods listed herein.

Each cylinder of engine 10 may include one or more intake valves and one or more exhaust valves. For example, cylinder 14 is shown including at least one intake poppet valve 250 and at least one exhaust poppet valve 256 located at an upper region of cylinder 14. In some embodiments, each cylinder of engine 10, including cylinder 14, may include at least two intake poppet valves and at least two exhaust poppet valves located at an upper region of the cylinder.

Intake valve 250 may be controlled by controller 12 by cam actuation via cam actuation system 251. Similarly, exhaust valve 256 may be controlled by controller 12 via cam actuation system 253. Cam actuation systems 251 and 253 may each include one or more cams and may utilize one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT) and/or variable valve lift (VVL) systems that may be operated by controller 12 to vary valve operation. The operation of intake valve 250 and exhaust valve 256 may be determined by valve position sensors (not shown) and/or camshaft position sensors 255 and 257, respectively. In alternative embodiments, the intake and/or exhaust valve may be controlled by electric valve actuation. For example, cylinder 14 may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including CPS and/or VCT systems. In still other embodiments, the intake and exhaust valves may be controlled by a common valve actuator or actuation system, or a variable valve timing actuator or actuation system.

Cylinder 14 can have a compression ratio, which is the ratio of volumes when piston 238 is at bottom center to top center. Conventionally, the compression ratio is in the range of 9:1 to 10:1. However, in some examples where different fuels are used, the compression ratio may be increased. This may happen, for example, when higher octane fuels or fuels with higher latent enthalpy of vaporization are used. The compression ratio may also be increased if direct injection is used due to its effect on engine knock.

In some embodiments, each cylinder of engine 10 may include a spark plug 292 for initiating combustion. Ignition system 290 can provide an ignition spark to combustion chamber 14 via spark plug 292 in response to spark advance signal SA from controller 12, under select operating modes. However, in some embodiments, spark plug 292 may be omitted, such as where engine 10 may initiate combustion by auto-ignition or by injection of fuel as may be the case with some diesel engines.

In some embodiments, each cylinder of engine 10 may be configured with one or more injectors for providing a knock control fluid thereto. In some embodiments, the knock control fluid may be a fuel, wherein the injector is also referred to as a fuel injector. As a non-limiting example, cylinder 14 is shown including one fuel injector 266. Fuel injector 266 is shown coupled directly to cylinder 14 for injecting fuel directly therein in proportion to the pulse width of signal FPW received from controller 12 via electronic driver 268. In this manner, fuel injector 166 provides what is known as direct injection (hereafter also referred to as “DI”) of fuel into combustion cylinder 14. While FIG. 2 shows injector 266 as a side injector, it may also be located overhead of the piston, such as near the position of spark plug 292. Such a position may improve mixing and combustion when operating the engine with an alcohol-based fuel due to the lower volatility of some alcohol-based fuels. Alternatively, the injector may be located overhead and near the intake valve to improve mixing. Fuel may be delivered to fuel injector 266 from a high pressure fuel system 8 including one or more fuel tanks 78, fuel pumps, and a fuel rail. Alternatively, fuel may be delivered by a single stage fuel pump at lower pressure, in which case the timing of the direct fuel injection may be more limited during the compression stroke than if a high pressure fuel system is used. Further, while not shown, fuel tanks 78 may have a pressure transducer providing a signal to controller 12. It will be appreciated that, in an alternate embodiment, injector 266 may be a port injector providing fuel into the intake port upstream of cylinder 14.

Fuel may be delivered by the injector to the cylinder during a single cycle of the cylinder. Further, the distribution and/or relative amount of fuel delivered from the injector may vary with operating conditions, such as aircharge temperature, as described herein below. Furthermore, for a single combustion event, multiple injections of the delivered fuel may be performed per cycle. The multiple injections may be performed during the compression stroke, intake stroke, or any appropriate combination thereof.

As described above, FIG. 1 shows only one cylinder of a multi-cylinder engine. As such each cylinder may similarly include its own set of intake/exhaust valves, fuel injector(s), spark plug, etc.

Fuel tanks 78 in fuel system 8 may hold fuel or knock control fluids with different qualities, such as different compositions. These differences may include different alcohol content, different water content, different octane, different heat of vaporizations, different fuel blends, different water contents, different flammability limits, and/or combinations thereof etc. In one example, knock control fluids with different alcohol contents could include one fuel being gasoline and the other being ethanol or methanol. Other alcohol containing fuels could be a mixture of alcohol and water, a mixture of alcohol, water, etc. In still another example, both fuels may be alcohol blends wherein the first fuel may be a gasoline alcohol blend with a lower ratio of alcohol than a gasoline alcohol blend of a second fuel with a greater ratio of alcohol, such as E10 (which is approximately 10% ethanol) as a first fuel and E85 (which is approximately 85% ethanol) as a second fuel. Additionally, the first and second fuels may also differ in other fuel qualities such as a difference in temperature, viscosity, octane number, latent enthalpy of vaporization etc.

Moreover, fuel characteristics of the fuel or knock control fluid stored in the fuel tank may vary frequently. The day to day variations in tank refilling can thus result in frequently varying fuel compositions, thereby affecting the fuel composition delivered by injector 166.

In addition to the fuel tanks, fuel system 8 may also include a reservoir 76 for storing a knock control fluid, herein windshield wiper fluid. While reservoir 76 is depicted as being distinct from the one or more fuel tanks 78, it will be appreciated that in alternate examples, reservoir 76 may be one of the one of more fuel tanks 78. Reservoir 76 may be coupled to direct injector 266 so that wiper fluid can be directly injected into cylinder 14. During some conditions, in response to an indication of knock, an engine controller may inject wiper fluid, being using as a knock control fluid, into the intake manifold, downstream of the intake throttle, to increase engine dilution and thereby control the untimely and unwanted detonation event. Alternatively, or additionally, in response to an indication of knock, the engine controller may directly inject wiper fluid, being using as a knock control fluid, into the engine cylinder to increase engine dilution and thereby control the untimely and unwanted detonation event

In some embodiments, the fuel system may also include a reservoir for storing water that is coupled to the direct injector so that water may be direct injected into the cylinder. As such, by injecting water, “liquid EGR” is provided, which enables substantial EGR benefits to be achieved. However, during conditions when liquid needs to be conserved, or when a back-up is required for when liquid EGR is not present, external EGR system may be added.

The engine may further include one or more exhaust gas recirculation passages for diverting at least a portion of exhaust gas from the engine exhaust to the engine intake. FIG. 2 shows a low pressure EGR (LP-EGR) system, but an alternative embodiment may include only a high pressure EGR (HP-EGR) system, or a combination of both LP-EGR and HP-EGR systems.

The LP-EGR is routed through LP-EGR passage 249 from downstream of turbine 276 to upstream of compressor 274. The amount of LP-EGR provided to intake manifold 244 may be varied by controller 12 via LP-EGR valve 252. The LP-EGR system may include LP-EGR cooler 258 to reject heat from the EGR gases to engine coolant, for example. When included, the HP-EGR system may route HP-EGR through a dedicated HP-EGR passage (not shown) from upstream of turbine 276 to downstream of compressor 274 (and upstream of intake throttle 262), via an HP-EGR cooler. The amount of HP-EGR provided to intake manifold 244 may be varied by controller 12 via an HP-EGR valve (not shown).

Under some conditions, the EGR system may be used to regulate the temperature of the air and fuel mixture within combustion chamber 14. Thus, it may be desirable to measure or estimate the EGR mass flow. For example, one or more sensors 259 may be positioned within LP-EGR passage 249 to provide an indication of one or more of a pressure, temperature, and air-fuel ratio of exhaust gas recirculated through the LP-EGR passage. Exhaust gas diverted through LP-EGR passage 249 may be diluted with fresh intake air at a mixing point located at the junction of LP-EGR passage 249 and intake passage 242. In some examples, where an air intake system (AIS) throttle is included in intake passage 242, upstream of compressor 274, by adjusting LP-EGR valve 252 in coordination with the air intake system throttle, a dilution of the EGR flow may be adjusted.

A percent dilution of the LP-EGR flow may be inferred from the output of a sensor in the engine intake gas stream. For example, a sensor 172 positioned downstream of LP-EGR valve 252, and upstream of main intake throttle 262, may be used so that the LP-EGR dilution at or close to the main intake throttle may be accurately determined. Sensor 172 may be, for example, an oxygen sensor. In addition, during selected conditions, sensor 172 may be used for estimating the alcohol content of fuel delivered to the engine, as well as the alcohol content and composition of a knock control fluid delivered to cylinder 14.

Controller 12 is shown in FIG. 2 as a microcomputer, including microprocessor unit 206, input/output ports 208, an electronic storage medium for executable programs and calibration values shown as read only memory chip 210 in this particular example, random access memory 212, keep alive memory 214, and a data bus. Controller 12 may receive various signals from sensors coupled to engine 10, in addition to those signals previously discussed, including measurement of inducted mass air flow (MAF) from mass air flow sensor 222; engine coolant temperature (ECT) from temperature sensor 216 coupled to cooling sleeve 218; a profile ignition pickup signal (PIP) from Hall effect sensor 220 (or other type) coupled to crankshaft 240; throttle position (TP) from a throttle position sensor; and manifold absolute pressure signal (MAP) from sensor 224. Engine speed signal, RPM, may be generated by controller 12 from signal PIP. Manifold pressure signal MAP from a manifold pressure sensor may be used to provide an indication of vacuum, or pressure, in the intake manifold. Still other sensors may include fuel level sensors and fuel composition sensors coupled to the fuel tank(s) of the fuel system. Controller 12 may also receive an operator request for windshield wiping via a dedicated sensor (not shown). In response to the signals received from the various sensors, the controller may operate various engine actuators. Example actuators include fuel injector 266, wiper motor 72, wiper injector 74, throttle 262, cams 251 and 253, etc. Storage medium read-only memory 210 can be programmed with computer readable data representing instructions executable by processor 206 for performing the methods described below as well as other variants that are anticipated but not specifically listed. Example routines that may be performed are elaborated with reference to FIGS. 4 and 7.

Next, FIG. 3 shows a schematic view of an example embodiment of an oxygen sensor 300 configured to measure a concentration of oxygen (O₂) in an aircharge stream. Sensor 300 may operate as intake oxygen sensor 172 or exhaust oxygen sensor 228 of FIGS. 1-2, for example. Sensor 300 comprises a plurality of layers of one or more ceramic materials arranged in a stacked configuration. In the embodiment of FIG. 3, five ceramic layers are depicted as layers 301, 302, 303, 304, and 305. These layers include one or more layers of a solid electrolyte capable of conducting ionic oxygen. Examples of suitable solid electrolytes include, but are not limited to, zirconium oxide-based materials. Further, in some embodiments, a heater 307 may be disposed in thermal communication with the layers to increase the ionic conductivity of the layers. While the depicted oxygen sensor is formed from five ceramic layers, it will be appreciated that the oxygen sensor may include other suitable numbers of ceramic layers.

Layer 302 includes a material or materials creating a diffusion path 310. Diffusion path 310 is configured to introduce intake gases into a first internal cavity 322 via diffusion. Diffusion path 310 may be configured to allow one or more components of exhaust gases, including but not limited to a desired analyte (e.g., O₂), to diffuse into internal cavity 322 at a more limiting rate than the analyte can be pumped in or out by pumping electrodes pair 312 and 314. In this manner, a stoichiometric level of O₂ may be obtained in the first internal cavity 322.

Sensor 300 further includes a second internal cavity 324 within layer 304 separated from the first internal cavity 322 by layer 303. The second internal cavity 324 is configured to maintain a constant oxygen partial pressure equivalent to a stoichiometric condition, e.g., an oxygen level present in the second internal cavity 324 is equal to that which the exhaust gas would have if the air-fuel ratio was stoichiometric. Herein, second internal cavity 324 may be referred to as a reference cell. As shown, the reference voltage is variable (e.g., between 0 and 1300 mV).

A pair of sensing electrodes 316 and 318 is disposed in communication with first internal cavity 322 and reference cell 324. The sensing electrodes pair 316 and 318 detects a concentration gradient that may develop between the first internal cavity 322 and the reference cell 324 due to an oxygen concentration in the intake air that is higher than or lower than the stoichiometric level. A high oxygen concentration may be caused by a lean charge mixture, while a low oxygen concentration may be caused by a rich charge mixture.

A pair of pumping electrodes 312 and 314 is disposed in communication with internal cavity 322, and is configured to electrochemically pump a selected gas constituent (e.g., O₂) from internal cavity 322 through layer 301 and out of sensor 300. Alternatively, the pair of pumping electrodes 312 and 314 may be configured to electrochemically pump a selected gas through layer 301 and into internal cavity 322. Herein, pumping electrodes pair 312 and 314 may be referred to as an O₂ pumping cell.

Electrodes 312, 314, 316, and 318 may be made of various suitable materials. In some embodiments, electrodes 312, 314, 316, and 318 may be at least partially made of a material that catalyzes the dissociation of molecular oxygen. Examples of such materials include, but are not limited to, electrodes containing platinum and/or silver.

The process of electrochemically pumping the oxygen out of or into internal cavity 322 includes applying a voltage V_(p) across pumping electrode pair 312 and 314. The pumping voltage V_(p) applied to the O₂ pumping cell pumps oxygen into or out of first internal cavity 322 in order to maintain a stoichiometric level of oxygen in the cavity pumping cell. The resulting pumping current I_(p) is proportional to the concentration of oxygen in the exhaust gas. A control system (not shown in FIG. 3) generates the pumping current signal I_(p) as a function of the intensity of the applied pumping voltage V_(p) required to maintain a stoichiometric level within the first internal cavity 322. Thus, a lean mixture will cause oxygen to be pumped out of internal cavity 322 and a rich mixture will cause oxygen to be pumped into internal cavity 322. Further, the output gain of the pumping current may be varied via the variable gain operational amplifier (e.g., op-amp). By varying the reference voltage and the output gain of the op-amp, the oxygen sensor may provide a higher resolution signal.

It should be appreciated that the oxygen sensor described herein is merely an example embodiment of an oxygen sensor, and that other embodiments of oxygen sensors may have additional and/or alternative features and/or designs.

Turning now to FIG. 4, an example routine 400 is shown for using an intake oxygen sensor (such as sensor 172 of FIGS. 1-2) for estimating the alcohol content and/or composition of an injected wiper fluid based on a change in pumping current of the intake oxygen sensor following injection of wiper fluid at two different gaseous percentages. Likewise, FIG. 7 depicts example routine 700 for using an exhaust oxygen sensor (such as sensor 228 of FIGS. 1-2) for estimating the alcohol content and/or composition of an injected wiper fluid based on a change in pumping current of the oxygen sensor following injection of wiper fluid at two different gaseous percentages. The methods enable the composition of the wiper fluid to be determined accurately, without the need for additional sensors, and also without the need for disrupting EGR flow, PCV flow, or purge flow.

At 402 and at 702, the method includes estimating and/or measuring engine operating conditions. These include, for example, engine speed, engine load, boost, ambient conditions (temperature, pressure, humidity), EGR, air-fuel ratio, etc.

At 404 and at 704, it may be determined if wiper fluid has been recently refilled in the wiper fluid reservoir. In particular, the wiper fluid composition estimation may be triggered by a recent wiper fluid refill event. This allows the composition of the available wiper fluid to be accurately known. Consequently, the wiper fluid may be more reliably used for knock control in addition to wiper washing functions. In alternate examples, the composition may be estimated in response to an operator request for wiper fluid composition estimation. For example, the composition of the wiper fluid may be determined periodically, such as once every threshold distance of vehicle travel, once every duration of engine operation or vehicle travel, once every threshold number of engine cycles, etc.

Herein, the wiper fluid (also referred to as a windshield washer fluid or just washer fluid) is a water-alcohol blend that includes no gasoline. In other words, the alcohol is the only source of hydrocarbons in the wiper fluid. In one example, the alcohol in the water-alcohol blend is one or more of ethanol, methanol, propanol, isopropanol, etc. It will be appreciated that while the present routine depicts the composition estimation of a wiper fluid to enable the fluid to be also leveraged as a knock control fluid, this is not meant to be limiting, and in other examples, the composition of an engine coolant fluid may be determined via the use of the intake oxygen sensor to enable the fluid to be also leveraged as a knock control fluid.

If wiper fluid has not been refilled in the reservoir, or if other wiper fluid composition estimation conditions have not been met, then at 406, the method includes continuing to operate the intake oxygen sensor as an oxygen sensor. Further, one or more engine operating parameters are adjusted based on the output of the oxygen sensor. As non-limiting examples, the output of the intake oxygen sensor may be used for EGR estimation and EGR control, as well as combustion air-fuel ratio control. For example, based on the estimated oxygen concentration of the intake aircharge, an amount of EGR delivered to the engine intake may be adjusted (e.g., to provide a desired engine dilution or a desired combustion air-fuel ratio). As another example, based on the estimated oxygen concentration of the intake aircharge, cylinder fueling may be adjusted.

Likewise, with reference to method 700, if wiper fluid has not been refilled in the reservoir, or if other wiper fluid composition estimation conditions have not been met, then at 706, the method includes continuing to operate the exhaust oxygen sensor as an oxygen sensor. Further, one or more engine operating parameters are adjusted based on the output of the oxygen sensor. As non-limiting examples, the output of the exhaust oxygen sensor may be used for exhaust oxygen estimation and combustion air-fuel ratio control. For example, based on the estimated oxygen concentration of the exhaust, cylinder fueling or air flow may be adjusted. As another example, the output of the exhaust oxygen sensor may be used for estimating the alcohol content of a fuel injected into and combusted in the engine cylinder.

If wiper fluid has been refilled in the reservoir, at 707, it may be determined if engine non-fueling conditions are present so as to enable wiper fluid composition estimation via the exhaust oxygen sensor. In one example, non-fueling conditions may be confirmed during a deceleration fuel shut-off event (DFSO) wherein cylinder fueling is deactivated during deceleration while at least one intake valve and exhaust valve continues to pump air through the cylinder. As such, the exhaust oxygen sensor may be used for estimating a wiper fluid composition only during non-fueling conditions. If non-fueling conditions are not met, the routine returns to 706.

If non-fueling conditions are confirmed in routine 700, or if wiper fluid has been refilled in the reservoir, wiper fluid composition estimation conditions may be considered met, then at 408 and 708, the method includes first injecting an amount (herein also referred to as the injection mass) of the wiper fluid at a first volume percentage. The first volume percentage represents a first gaseous volume percentage of the washer fluid in the volume of intake air (in mole percentage). The first volume percentage may be achieved by injecting a first amount of fluid at a first mass air flow rate (that is, at a first setting of the intake throttle). The first amount of washer fluid injected may be based on a predetermined value that is chosen to provide an optimized signal to noise ratio while using the least amount of washer fluid possible so that the washer fluid is not wasted. In one example, washer fluid is injected at the first volume percentage into the intake passage, downstream of the intake throttle (and upstream of the intake valve), such as in the case where the estimation is performed via the intake oxygen sensor. In another example, washer fluid is injected at the first volume percentage directly into the cylinder, such as in the case where the estimation is performed via the exhaust oxygen sensor.

At 410 and at 710, a lower pumping voltage (herein also called as the lower reference voltage) (V₁) is applied to the intake or exhaust oxygen sensor. The first pumping voltage may be a lower reference voltage that pumps oxygen from the oxygen pumping cell, but may have a low enough value so as to not dissociate water (e.g., H₂O) molecules in the pumping cell (e.g., V₁=450 mV). At 412 and at 712, upon applying the first voltage to the pumping cell after the injection of the wiper fluid at the first gaseous volume percentage, a first pumping current (I₁) or first oxygen sensor reading (such as a first intake oxygen sensor (IAO2) reading in routine 400 or a first exhaust oxygen sensor (UEGO) reading in routine 700) is noted. Herein, the first sensor reading may be indicative of an amount of oxygen that either reacted with the sensing element of the oxygen sensor, or was displaced due to the dilution effect of the water.

At 414 and 714, the methods include injecting the washer fluid/wiper fluid (e.g. into the intake manifold or directly into the cylinder) at a second volume percentage. The second volume percentage represents a second, different (e.g., higher or lower) gaseous volume percentage of the washer fluid in the volume of intake air (in mole percentage). The second volume percentage may be achieved by injecting a second amount of fluid at the first mass air flow rate (that is, at the first setting of the intake throttle). Alternatively, the second volume percentage may be achieved by injecting the first (same) amount of fluid at a second, different (e.g., higher or lower) mass air flow rate (that is, at a second, different setting of the intake throttle). The second amount of washer fluid injected may be based on a predetermined value that is chosen to provide an optimized signal to noise ratio while using the least amount of washer fluid possible so that the washer fluid is not wasted.

At 416 and 716, the lower pumping voltage (herein also called as the lower reference voltage) (V₁) is applied to the intake or exhaust oxygen sensor. At 418 and 718, upon applying the first voltage to the pumping cell after the injection of the wiper fluid at the second volume percentage, a second pumping current (I₂) or second intake or exhaust oxygen sensor (IAO2 or UEGO) reading is noted. Herein, the second sensor reading also may be indicative of an amount of oxygen that either reacted with the sensing element of the oxygen sensor, or was displaced due to the dilution effect of the water. However, in the case of both the first and the second sensor readings, an offset in the pumping currents resulting from the presence of diluents and hydrocarbons from EGR, purge, and PCV flow remains the same. This common offset is leveraged in the routines to determine the alcohol content/composition of the wiper fluid accurately without requiring active changes to purge, PCV, or EGR flow.

At 420 and 720, a transfer function may be determined for the wiper fluid based on the intake manifold airflow level (as determined, for example, based on the output of a MAF sensor), as well as the wiper fluid injection mass. The transfer function may represent an expected change in pumping current of the intake/exhaust oxygen sensor with injection mass, at a given reference voltage (herein the lower reference voltage). This change is then compared to a baseline reading of the oxygen concentration when no washer fluid is injected. Similarly, the manifold airflow may be interpreted from a MAP sensor and a look-up table that determines the air mass flow rate in a speed-density system.

At 422 and at 722, the methods include calculating a first and a second concentration of the wiper fluid in the intake airstream based on the first and second sensor readings, respectively. As such, the first and second concentrations may also reflect first and second concentrations of alcohol (from the wiper fluid) in the intake airstream. Specifically, the first and second wiper fluid concentrations in the intake air are determined based on the first and second sensor readings respectively, and further based on the determined transfer function, the injection mass, and the first and second volume percentages, respectively.

In particular, the controller may estimate a first concentration or proportion of wiper fluid in the intake air by learning a first portion of the change in the first pumping current due to a water content of the fluid, while learning a second portion of the change in first pumping current due to an alcohol content of the blend following the injection of the wiper fluid at the first volume percentage. Likewise, the controller may estimate a second concentration or proportion of wiper fluid in the intake air by learning a first portion of the change in the second pumping current due to a water content of the fluid, while learning a second portion of the change in second pumping current due to an alcohol content of the blend. In each case, at least the second portion may be estimated based on the sensor pumping current following the applying of the reference voltage and further based on the fluid injection mass and the determined transfer function.

In one example, injection concentration of wiper fluid in the intake air may be determined following each injection based on the corresponding pumping current and the transfer function. In one example, the computer readable storage medium of the control system receiving communication from the sensor may include instructions for identifying the wiper fluid content in the intake air by referring to a graph depicting examples of the relationship between change in oxygen sensor output and injection mass with change in percent alcohol content of the intake air (as discussed below with reference to FIG. 5), the graph data stored on the computer readable storage medium in the form of a lookup table, for example. Therein, as the amount of injected wiper fluid increases for a given injection, the amount of water estimated by the intake oxygen sensor may correspondingly decrease. As shown in FIG. 5, for a given mass of washer fluid injected into the intake air stream, a higher change (delta) in intake oxygen sensor output will reflect a higher methanol concentration in the wiper fluid injected into the intake airstream. Consequently, the change in oxygen percentage (delta 02%) will be closer to the 100% MeOH line, and the engine controller may determine/identify the methanol concentration that corresponds to that operating point.

As such, when the mass of the injected washer fluid is held constant, the wiper fluid concentration in the intake airstream will also be constant. During such conditions, a higher change (delta) in intake oxygen sensor output reflects a higher methanol concentration in the wiper fluid injected in the intake airstream. The engine controller may identify a point on the x axis of map 500 of FIG. 5, and determine the corresponding change in methanol % in wiper fluid as delta O2% increases. In particular, as one goes up along the y-axis for a fixed point on the x-axis, increasing methanol concentrations are determined in the washer fluid.

In particular, Applicants have recognized that the effect of the water component of the water-alcohol blend on the oxygen sensor pumping current is distinct from the effect of the alcohol component (including the alcohol content and the alcohol type) of the water-alcohol blend on the oxygen sensor pumping current. For example, injecting 1% water (by volume) into intake air results in a 0.2% reduction in oxygen concentration as measured by the oxygen sensor since it has a dilution effect on the oxygen concentration. However, injecting 1% methanol (by volume) into intake air results in a 1.5% reduction in oxygen concentration as measured by the oxygen sensor due to methanol combusting with the oxygen at the oxygen sensor's sensing element as indicated below.

CH₃OH+O₂=CO₂+H₂O

Hence, if a 2% of the washer fluid (water+methanol) mixture is injected, this will result in a total reduction in oxygen of 2.5% (in this example), 0.2/1.7 or 11.7% of that reduction is due to water, and a remaining 1.5/1.7 or 88.3% of that reduction is due to methanol.

Thus, learning the first portion may include determining a first value of methanol-to-water concentration in the blend (based on the change in pumping current). Further, learning the second portion may include determining a second value of methanol-to-water concentration in the blend that is learned based on the monitored change in pumping current and further based on the amount of water-alcohol blend injected. Herein, the second value may be reflective of a base concentration of oxygen in the ambient air. In addition, the controller may compare the first value to the second value.

As an example, the controller may reference a look-up table or a map, such as the example map of FIG. 5, to preliminarily estimate the alcohol concentration (or wiper fluid concentration) in the intake air. The map may be a 3D map requiring 2 inputs, the mass of fluid injected and the change in intake oxygen sensor pumping current, to provide an output regarding the percentage of alcohol in the intake air stream.

Referring to FIG. 5, map 500 depicts one such example map. In particular, map 500 depicts change in intake oxygen sensor along the y-axis (Delta 02%) and injection mass of washer fluid (M_washer_fluid_inj) along the y-axis. Herein, the washer fluid is a water-methanol blend that includes no gasoline. The map is calibrated for 0% methanol (MeOH) and 100% methanol, as well as one or more intermediate methanol percentages. As can be seen, for a first injection at a first volume percentage (such as a first mass flow rate), a first change in oxygen sensor output (Delta_O2_1) is observed, and for a second injection at a second volume percentage (such as a second mass flow rate), a second change in oxygen sensor output (Delta_O2_2) is observed. Using the map, the methanol percentage (Methanol_pct) may then be estimated as: Methanol_pct=fn (delta_O2, M_washer_fluid_inj). In particular, a first wiper fluid concentration/percentage P1 is estimated corresponding to the first oxygen sensor output (Delta_O2_1) and a second wiper fluid concentration/percentage P2 is estimated corresponding to the second oxygen sensor output (Delta_O2_2). Thus, using a map such as the map of FIG. 5, a controller may be able to estimate the alcohol percentage or wiper fluid concentration of the intake air. Then, by correcting for a common offset realized at different wiper fluid injection percentage, the wiper fluid composition may be determined. In particular, the inventors have recognized that since the alcohol composition of the wiper fluid stays constant, a relative change in the oxygen sensor output due to the presence of diluents (such as humidity, PCV or purge flow, or EGR flow) can be estimated by comparing the change at two different fluid percentages. In doing so, the need for disabling EGR flow or purge flow or PCV for accurate wiper fluid composition estimation may not be required. In other words, wiper fluid composition estimation can be done without needing to compensate for noise factors.

Additionally or alternatively, the controller may use a map, such as map 800 of FIG. 8 to correlate a change in intake or exhaust concentration (as determined based on the output of the intake or exhaust oxygen sensor) with the mole percentage of gaseous fluid in the intake air stream.

Returning to FIGS. 4 and 7, at 424 and 724, the method includes normalizing the estimated first and second alcohol percentages P1 and P2 based on the corresponding first and second volume percentages. At 426 and 726, the method includes determining a common offset in the percentages due to the presence of diluents in the intake air based on the normalized readings. For example, the percentages P1 and P2 may be plotted and the offset may be determined based on the slope of a line fitted to both the readings. At 428 and 728, the method includes determining the percentage of alcohol in the wiper fluid based on the learned offset.

As an example, the controller may plot a map, such as the example map of FIG. 6, to estimate the offset. Referring to FIG. 6, map 600 depicts mass flow rate along the x-axis and the estimated alcohol percentage along the y-axis. P1 and P2 described with reference to FIG. 5 are shown plotted on line 602. The offset is then determined based on slope 604 of line 602.

For P1:Y1=m*X1+Offset

For P2: Y2=m*X2+Offset

Since m and the Offset are the same for both the points, the controller can determine the effect of humidity, intake hydrocarbons, and other diluents (that is, the offset) using the two measurements as:

m=(Y2−Y1)/(X2−X1)

m can then be directly related to the methanol concentration of the knock control fluid.

Returning to FIGS. 4 and 7, at 430 and 730, upon determining the composition (and alcohol percentage) of the wiper fluid, an octane value of the fluid is updated. In addition, a fuel octane estimate for the engine system may be updated. For example, an octane modifier term using during feed-forward control of knock may be updated. In one example, the updating includes increasing the octane value as the alcohol (ethanol or methanol) content of the wiper fluid increases or as the water content of the wiper fluid decreases.

At 432 and 732, upon confirming the composition of the wiper fluid, the fluid may be used as a knock control fluid as required. For example, in response to an indication of knock, or in anticipation of possible knock, an amount of the wiper fluid may be injected based on the octane requirement of the engine (to address the knock) relative to the updated octane value of the fluid.

At 434 and 734, one or more engine operating parameters are adjusted based on the updated wiper fluid and fuel octane estimate. For example, a base spark timing applied may be adjusted (e.g., advanced from MBT). As another example, borderline spark value may be adjusted (e.g., advanced). As still another example, one or more of an EGR schedule, VCT schedule, variable compression ratio, dual fuel injection schedule, etc., may be adjusted.

Upon completing the wiper fluid composition estimation via the intake oxygen sensor, the method may return to 406 wherein the sensor may resume being operated for oxygen sensing for the purposes of EGR control, air-fuel ratio control, and the like. Likewise, upon completing the wiper fluid composition estimation via the exhaust oxygen sensor, the method may return to 706 wherein the sensor may resume being operated for oxygen sensing for the purposes of air-fuel ratio control, and the like.

In this way, wiper fluid composition estimation can be improved, and interference in estimation due to the presence of diluents in the intake air is more reliably corrected for. The technical effect of comparing the oxygen sensor output following wiper fluid injection at different volume percentages is that a common relative change in the oxygen sensor output due to the presence of diluents can be used to estimate wiper fluid composition without needing to adjust diluent flow or estimate diluent concentration separately. The technical effect of this more reliable estimation is that the use of the fluid can be expanded to other functions. For example, the more accurate and reliable composition estimation may allow for improved usage of wiper fluid outside of windshield wiping, or of engine coolant outside of engine cooling. In particular, the wiper fluid and/or the engine coolant may be used more reliably and consistently as a knock control fluid for addressing knock. The technical effect of improving the usage of a water-alcohol blend in the mitigation of knock is that the octane requirements of fuel can be reduced, while knock is addressed, allowing more power to be gained from the engine. In addition, by reducing the need for spark retard, fuel economy benefits are achieved.

One example engine method comprises: injecting a water-alcohol blend into an engine intake initially at a first volume percentage and then at a second, different volume percentage; applying a reference voltage to an oxygen sensor and monitoring a change in pumping current of the sensor following each injecting; learning a first portion of the change in pumping current due to a water content of the blend; learning a second portion of the change in pumping current due to an alcohol content of the blend; and learning a third portion of the change in pumping current due to diluents in intake air. Additionally or optionally, the example method further comprises learning a composition of the blend based on the learned first portion, second portion, and third portion, and further based on the injection amount. Any or all of the preceding examples additionally or optionally further comprise adjusting an engine operating parameter based on the learned composition, the engine operating parameter including one or more of a fuel octane estimate and a fuel injection amount. In any or all of the preceding examples, additionally or optionally, the first volume percentage includes a first amount of fluid injection at a first intake throttle position and the second volume percentage includes a second amount of fluid injection at the first intake throttle position, and the diluents in intake air include one or more of ambient humidity, canister purge hydrocarbons, and crankcase ventilation hydrocarbons. In any or all of the preceding examples, additionally or optionally, the first volume percentage includes a first amount of fluid injection at a first intake throttle position and the second volume percentage includes the first amount of fluid injection at the first intake throttle position. In any or all of the preceding examples, additionally or optionally, the blend includes no gasoline and wherein the alcohol includes one or more of ethanol and methanol. In any or all of the preceding examples, additionally or optionally, the applying includes applying a voltage that does not dissociate water molecules. In any or all of the preceding examples, additionally or optionally, learning the first portion and second portion includes determining a first concentration of the fluid in intake air based on a first change in pumping current following injecting at the first volume percentage and determining a second concentration of the fluid in intake air based on a second change in pumping current following injecting at the second volume percentage. In any or all of the preceding examples, additionally or optionally, learning the third portion includes normalizing the first concentration based on the first volume percentage while normalizing the second concentration based on the second volume percentage; learning an offset based on the normalized first and second concentrations; and learning an alcohol content of the fluid based on the learned offset. In any or all of the preceding examples, additionally or optionally, the method is performed responsive to selected conditions being identified, the selected conditions including following refilling of the water-alcohol blend in a reservoir when the oxygen sensor is an intake oxygen sensor, the selected conditions including following refilling of the water-alcohol blend in a reservoir and deceleration fuel shut-off conditions when the oxygen sensor is an exhaust oxygen sensor. In any or all of the preceding examples, additionally or optionally, the water-alcohol blend includes one of wiper fluid and washer fluid.

Another example method for an engine, comprises injecting an amount of water-alcohol blend into an engine at a first intake mass flow rate, and estimating a first alcohol concentration in intake air based on a first change in pumping current of an oxygen sensor; then, injecting the amount of water-alcohol blend into the engine at a second, different intake mass flow rate, and estimating a second alcohol concentration in the intake air based on a second change in pumping current of the oxygen sensor; learning a diluent concentration in the intake air based on the first and second change in pumping current; and learning a composition of the water-alcohol blend based on each of the first and second change in pumping currents and the learned diluent concentration. In any or all of the preceding examples, additionally or optionally, the method further comprises, following each injecting, applying a reference voltage to the oxygen sensor that does not dissociate water molecules, and wherein the oxygen sensor is one of an intake oxygen sensor and an exhaust oxygen sensor. In any or all of the preceding examples, additionally or optionally, learning the composition of the water-alcohol blend includes distinguishing a first portion of the first and second change in pumping current due to a water content of the water-alcohol blend from a second portion of the first and second change in pumping current due to an alcohol content of the water-alcohol blend, and a third portion of the first and second change in pumping current due to the diluent concentration in the intake air. In any or all of the preceding examples, additionally or optionally, when the oxygen sensor is the intake oxygen sensor, the injecting is responsive to refilling of the water-alcohol blend in a knock control fluid tank, and the injecting includes injecting into an intake manifold, downstream of an intake throttle and upstream of the intake oxygen sensor, and wherein when the oxygen sensor is the exhaust oxygen sensor, the injecting is responsive to refilling of the water-alcohol blend in a knock control fluid tank and fueling of a cylinder being deactivated, and the injecting includes directly injecting into the cylinder, the water-alcohol blend including wiper fluid. In any or all of the preceding examples, additionally or optionally, the composition is further based on the amount of injection, the method further comprising, adjusting a knock-mitigating spark retard amount based on the learned composition of the water-alcohol blend. In any or all of the preceding examples, additionally or optionally, the method further comprises, in response to an indication of knock in an engine cylinder, directly injecting the water-alcohol blend into the cylinder, an amount of the directly injecting adjusted based on the learned composition of the water-alcohol blend.

Another example engine system comprises an engine including an intake manifold for receiving intake air; a first injector for injecting fuel into an engine cylinder; a second injector for injecting a knock control fluid into the intake manifold, downstream of an intake throttle; an EGR system including a passage for recirculating exhaust residuals from downstream of the turbine to upstream of the compressor via an EGR valve; an oxygen sensor coupled to the intake manifold, downstream of the intake throttle and downstream of the EGR valve; and a controller with computer readable instructions stored on non-transitory memory for: injecting knock control fluid into the intake manifold at a first gaseous volume percentage, then applying a reference voltage to the oxygen sensor and measuring a first change in pumping current; then injecting the knock control fluid into the intake manifold at a second, different gaseous volume percentage, then applying the reference voltage to the oxygen sensor and measuring a second change in pumping current; estimating a diluent content of the intake air based on each of the first and second change in pumping current and the first and second gaseous volume percentage; and estimating a composition of the knock control fluid based on each of an injection mass, the first and second change in pumping current, and the estimated diluent content. In any or all of the preceding examples, additionally or optionally, the knock control fluid includes water and alcohol and no fuel, and wherein the controller estimates the diluent content by calculating an offset based on a difference between the first and second change in pumping current relative to a difference between the first and second gaseous volume percentage, and wherein the controller estimates the composition by calculating a first portion of each of the first and second change in pumping current due to a water content of the knock control fluid, calculating a second portion of each of the first and second change in pumping current due to an alcohol content of the knock control fluid, and applying the offset to the each of the calculated first and second portion. In any or all of the preceding examples, additionally or optionally, the controller includes further instructions for updating an engine fuel octane estimate based on the estimated composition of the knock control fluid; and adjusting each of a spark timing and a borderline spark value applied responsive to knock based on the updated fuel octane estimate, the adjusting including retarding spark timing from a base spark timing, and advancing borderline spark towards MBT as the fuel octane estimate increases.

Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the engine control system, where the described actions are carried out by executing the instructions in a system including the various engine hardware components in combination with the electronic controller.

It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure. 

1. An engine method, comprising: injecting a water-alcohol blend into an engine intake initially at a first volume percentage and then at a second, different volume percentage; applying a reference voltage to an oxygen sensor and monitoring a change in pumping current of the sensor following each injecting; learning a first portion of the change in pumping current due to a water content of the blend; learning a second portion of the change in pumping current due to an alcohol content of the blend; and learning a third portion of the change in pumping current due to diluents in intake air.
 2. The method of claim 1, further comprising, learning a composition of the blend based on the learned first portion, second portion, and third portion, and further based on the injection amount.
 3. The method of claim 2, further comprising, adjusting an engine operating parameter based on the learned composition, the engine operating parameter including one or more of a fuel octane estimate and a fuel injection amount.
 4. The method of claim 1, wherein the first volume percentage includes a first amount of fluid injection at a first intake throttle position and the second volume percentage includes a second amount of fluid injection at the first intake throttle position, and wherein the diluents in intake air include one or more of ambient humidity, canister purge hydrocarbons, and crankcase ventilation hydrocarbons.
 5. The method of claim 1, wherein the first volume percentage includes a first amount of fluid injection at a first intake throttle position and wherein the second volume percentage includes the first amount of fluid injection at the first intake throttle position.
 6. The method of claim 1, wherein the blend includes no gasoline and wherein the alcohol includes one or more of ethanol and methanol.
 7. The method of claim 1, wherein the applying includes applying a voltage that does not dissociate water molecules.
 8. The method of claim 1, wherein learning the first portion and second portion includes determining a first concentration of the fluid in intake air based on a first change in pumping current following injecting at the first volume percentage and determining a second concentration of the fluid in intake air based on a second change in pumping current following injecting at the second volume percentage.
 9. The method of claim 8, wherein learning the third portion includes normalizing the first concentration based on the first volume percentage while normalizing the second concentration based on the second volume percentage learning an offset based on the normalized first and second concentrations; and learning an alcohol content of the fluid based on the learned offset.
 10. The method of claim 1, wherein the method is performed responsive to selected conditions being identified, the selected conditions including following refilling of the water-alcohol blend in a reservoir when the oxygen sensor is an intake oxygen sensor, the selected conditions including following refilling of the water-alcohol blend in a reservoir and deceleration fuel shut-off conditions when the oxygen sensor is an exhaust oxygen sensor.
 11. The method of claim 1, wherein the water-alcohol blend includes one of wiper fluid and washer fluid.
 12. A method for an engine, comprising: injecting an amount of water-alcohol blend into an engine at a first intake mass flow rate, and estimating a first alcohol concentration in intake air based on a first change in pumping current of an oxygen sensor; then, injecting the amount of water-alcohol blend into the engine at a second, different intake mass flow rate, and estimating a second alcohol concentration in the intake air based on a second change in pumping current of the oxygen sensor; learning a diluent concentration in the intake air based on the first and second change in pumping current; and learning a composition of the water-alcohol blend based on each of the first and second change in pumping currents and the learned diluent concentration.
 13. The method of claim 12, further comprising: following each injecting, applying a reference voltage to the oxygen sensor that does not dissociate water molecules, and wherein the oxygen sensor is one of an intake oxygen sensor and an exhaust oxygen sensor.
 14. The method of claim 12, wherein learning the composition of the water-alcohol blend includes distinguishing a first portion of the first and second change in pumping current due to a water content of the water-alcohol blend from a second portion of the first and second change in pumping current due to an alcohol content of the water-alcohol blend, and a third portion of the first and second change in pumping current due to the diluent concentration in the intake air.
 15. The method of claim 13, wherein when the oxygen sensor is the intake oxygen sensor, the injecting is responsive to refilling of the water-alcohol blend in a knock control fluid tank, and the injecting includes injecting into an intake manifold, downstream of an intake throttle and upstream of the intake oxygen sensor, and wherein when the oxygen sensor is the exhaust oxygen sensor, the injecting is responsive to refilling of the water-alcohol blend in a knock control fluid tank and fueling of a cylinder being deactivated, and the injecting includes directly injecting into the cylinder, the water-alcohol blend including wiper fluid.
 16. The method of claim 12, wherein the composition is further based on the amount of injection, the method further comprising, adjusting a knock-mitigating spark retard amount based on the learned composition of the water-alcohol blend.
 17. The method of claim 12, further comprising, in response to an indication of knock in an engine cylinder, directly injecting the water-alcohol blend into the cylinder, an amount of the directly injecting adjusted based on the learned composition of the water-alcohol blend.
 18. An engine system, comprising: an engine including an intake manifold for receiving intake air; a first injector for injecting fuel into an engine cylinder; a second injector for injecting a knock control fluid into the intake manifold, downstream of an intake throttle; an EGR system including a passage for recirculating exhaust residuals from downstream of the turbine to upstream of the compressor via an EGR valve; an oxygen sensor coupled to the intake manifold, downstream of the intake throttle and downstream of the EGR valve; and a controller with computer readable instructions stored on non-transitory memory for: injecting knock control fluid into the intake manifold at a first gaseous volume percentage, then applying a reference voltage to the oxygen sensor and measuring a first change in pumping current; then injecting the knock control fluid into the intake manifold at a second, different gaseous volume percentage, then applying the reference voltage to the oxygen sensor and measuring a second change in pumping current; estimating a diluent content of the intake air based on each of the first and second change in pumping current and the first and second gaseous volume percentage; and estimating a composition of the knock control fluid based on each of an injection mass, the first and second change in pumping current, and the estimated diluent content.
 19. The system of claim 18, wherein the knock control fluid includes water and alcohol and no fuel, and wherein the controller estimates the diluent content by calculating an offset based on a difference between the first and second change in pumping current relative to a difference between the first and second gaseous volume percentage, and wherein the controller estimates the composition by calculating a first portion of each of the first and second change in pumping current due to a water content of the knock control fluid, calculating a second portion of each of the first and second change in pumping current due to an alcohol content of the knock control fluid, and applying the offset to the each of the calculated first and second portion.
 20. The system of claim 18, wherein the controller includes further instructions for: updating an engine fuel octane estimate based on the estimated composition of the knock control fluid; and adjusting each of a spark timing and a borderline spark value applied responsive to knock based on the updated fuel octane estimate, the adjusting including retarding spark timing from a base spark timing, and advancing borderline spark towards MBT as the fuel octane estimate increases. 